This invention relates to dental prophylaxis angles (commonly referred to as prophy angles). It has particular application to a prophy angle which need not be lubricated even after repeated autoclave cycles. It also has more general application to making a simple prophy angle with a particularly effective driven gear and thrust bearing for its driven gear.
Prophy angles currently available are either low-cost disposable prophy angles which are discarded after each use or else expensive reusable metal prophy angles which require a considerable amount of care to maintain. A reusable angle must not only be autoclaved between uses or procedures to ensure that the angle is sterile for the next procedure, but it must be maintained. Reusable angles need to be lubricated to run smoothly. The lubrication, however, breaks down and is lost over time through use and because of the autoclaving. Reusable angles must therefore be disassembled periodically to be lubricated. Some manufacturers recommend that prophy angles be lubricated after every ten hours of use. If the angle is not lubricated, the angle will eventually seize up and become inoperable. Through use, debris may also find its way into the angle's head. This debris can interfere with the operation of the angle's gears, and can ultimately ruin the gears. The angle must therefore also be cleaned periodically, to remove any debris, such as grit, which may have found its way into the angle. Many dentists and hygienists do not lubricate and clean their prophy angles on a regular schedule. If the angles are not lubricated and cleaned periodically, they will eventually fail.
An example of an expensive, high-quality reusable prophy angle is the TS2.TM. angle sold by Young Dental Manufacturing Company of Earth City, Mo. This angle is shown in FIG. 1. All of the parts are machined from bronze and stainless steel. A body B terminates in an externally threaded stud B1. A drive gear member D includes a shaft DS rotatably mounted in an axial bore of the body and a drive gear DG butted against the end of the stud B1. A head part H is threaded onto the stud B1. The head part includes an axial bore HB and a bore extension HE. A post P is press fitted into the bore extension HE. The post P acts as a thrust bearing for a driven gear Dn. The driven gear Dn includes a gear part DnG and an upwardly-extending internally threaded bur tube DnT. A cap C is threaded into the open end of the head bore and forms radial bearings for the driven gear. A stem CS on the outside of the cap terminates in an externally beveled knife edge, a short distance above the top of the bur tube. Specially designed dental tools, such as prophy cups manufactured by Young Dental Manufacturing Company, when they are screwed into the bur tube DnT, form a seal with the stem CS and prevent intrusion of material from the patient's mouth into the angle. One manner of forming the seal is described in my U.S. Pat. No. 5,484,284.
An alternative to single-use disposable prophy angles and expensive reusable angles has been proposed in Wiseman, U.S. Pat. No. 3,163,934. That patent discloses a relatively low-cost prophy angle whose body, cap, and drive shaft bearing are made of polypropylene, and whose drive gear, driven gear, bearing-locking collar, and ball thrust bearing are made of metal. A small quantity of silicone lubricant is packed into the head (nose) of the angle. Although this angle is designed to be sealed and to be repeatedly sterilized, it is not sufficiently sealed to prevent intrusion of materials from the patient's mouth or leakage of lubricant during use, and it does not lend itself to repeated autoclaving. Moreover, its construction does not lend itself to precise alignment of the moving parts, thereby increasing the difficulty of making the instrument run smoothly, quietly, and reliably. The construction requires seven separate parts and relatively complicated assembly.